1. Field of the Invention
The present invention relates generally to an electronically controlled, high resolution light source, and more particularly, to a thin film electroluminescent (TFEL) edge emitter structure having a light emitting face at an angle greater than ninety degrees relative to a street defined along the forward edge of the substrate of the TFEL edge emitter structure.
2. Description of the Prior Art
Electroluminescence is a phenomena which occurs in certain materials from the passage of an electric current through the material. The electric current excites the electrons of the dopant in the light emitting material to higher energy levels. Emission of radiation thereafter occurs as the electrons emit or give up the excitation energy and fall back to lower energy levels. Such electrons can only have certain discrete energies. Therefore, the excitation energy is emitted or radiated at specific wavelengths depending on the particular material. TFEL devices that employ the electroluminescence phenomena have been devised in the prior art. It is well known to utilize a TFEL device to provide an electronically controlled, high resolution light source. One arrangement which utilizes the TFEL device to provide the light source is a flat panel display system such as disclosed in U.S. Pat. Nos. to Asars et al (4,110,664) and Luo et al (4,006,383), assigned to the assignee of the present invention. In a TFEL flat panel display system, light emissions are produced substantially normal to a face of the device and so provide the light source at the device face. Another arrangement utilizing the TFEL device to provide the light source is a line array, or edge, emitter, such as disclosed in a U.S. Pat. No. to Kun et al (4,535,341), also assigned to the assignee of the present invention. In a TFEL edge emitter system, light emissions are produced substantially normal to an edge of the TFEL device and so provide the light source at the device edge. Edge emissions by the TFEL edge emitter system are typically 30 to 40 times brighter than the face emissions by the TFEL flat panel display system under approximately the same excitation conditions.
From the above discussion, it can be appreciated that the TFEL edge emitter system of the Kun et al patent potentially provides a high resolution light source promising orders of magnitude of improved performance over the TFEL flat panel face emitter system in terms of light emission brightness. For the TFEL edge emitter device to be able to reach its full commercial potential, it must be capable of maximizing the amount of light coming from the light emitting surface. Since the zone of light emerging from the TFEL structure through its light emitting surface or face has a slightly divergent pattern, a focussing lens is typically disposed forwardly of the light emitting face to intercept and intensify the light coming form the ninety-degree light emitting face.
However, as a result of present techniques used in fabricating TFEL edge emitter devices, a front portion of the substrate of the TFEL structure extends forwardly of the light emitting face of the TFEL structure so as to define a street which is disposed at approximately ninety degrees to the TFEL light emitting face. The presence of the street on the substrate interferes with the lower divergent portion of the zone of light and thereby reduces the total amount of light emerging from the ninety-degree light emitting face of the TFEL light emitting structure.
Consequently, a need exists for a way to compensate for the presence of the substrate street so as to avoid interference by it with the emergent zone of light.